This invention relates to the field of downhole turbines used in drilling. More specifically, the invention relates to controlling the rotational velocity of downhole turbines.
Previous attempts at controlling downhole turbine speed were performed by diverting a portion of the drilling fluid away from the turbine. It was believed that the diversion of drilling fluid away from the turbine results in less torque on the turbine itself. However, this technique may also require the additional expense of having to over design the turbine to ensure that sufficient torque is delivered when fluid flow is restricted.
U.S. Pat. No. 5,626,200 to Gilbert et al., which is herein incorporated by reference for all that it contains, discloses a logging-while-drilling tool for use in a wellbore in which a well fluid is circulated into the wellbore through a hollow drill string. In addition to measurement electronics, the tool includes an alternator for providing power to the electronics, and a turbine for driving the alternator. The turbine blades are driven by the well fluid introduced into the hollow drill string. The tool also includes a deflector to deflect a portion of the well fluid away from the turbine blades.
U.S. Patent No. 5,839,508 to Tubel et al., which is herein incorporated by reference for all that it contains, discloses an electrical generating apparatus which connects to the production tubing. In a preferred embodiment, this apparatus includes a housing having a primary flow passageway in communication with the production tubing. The housing also includes a laterally displaced side passageway communicating with the primary flow passageway such that production fluid passes upwardly towards the surface through the primary and side passageways. A flow diverter may be positioned in the housing to divert a variable amount of the production fluid from the production tubing and into the side passageway. In accordance with an important feature of this invention, an electrical generator is located at least partially in or along the side passageway. The electrical generator generates electricity through the interaction of the flowing production fluid.
U.S. Pat. No. 4,211,291 to Kellner, which is herein incorporated by reference for all it contains, discloses a drill fluid powered hydraulic system used for driving a shaft connected to a drill bit. The apparatus includes a hydraulic fluid powered motor actuated and controlled by hydraulic fluid. The hydraulic fluid is supplied to the hydraulic fluid powered motor through an intermediate drive system actuated by drill fluid. The intermediate drive system is provided with two rotary valves and two double sided accumulators. One of the rotary valves routes the hydraulic fluid to and from the accumulators from the drill fluid supply and from the accumulators to the drill bit. The rotary valves are indexed by a gear system and Geneva drive connected to the motor or drill shaft. A heat exchanger is provided to cool the hydraulic fluid. The heat exchanger has one side of the exchange piped between the drill fluid inlet and the drill fluid rotary valve and the other side of the exchange piped between the hydraulic fluid side of the accumulators and the hydraulic fluid rotary valve.
U.S. Pat. No. 4,462,469 to Brown, which is herein incorporated by reference for all that it contains, discloses a motor for driving a rotary drilling bit within a well through which mud is circulated during a drilling operation, with the motor being driven by a secondary fluid which is isolated from the circulating mud but derives energy therefrom to power the motor. A pressure drop in the circulating mud across a choke in the drill string is utilized to cause motion of the secondary fluid through the motor. An instrument which is within the well and develops data to be transmitted to the surface of the earth controls the actuation of the motor between different operation conditions in correspondence with data signals produced by the instrument, and the resulting variations in torque in the drill string and/or the variations in torque in the drill string and/or the variations in circulating fluid pressure are sensed at the surface of the earth to control and produce a readout representative of the down hole data.
U.S. Pat. No. 5,098,258 to Barnetche-Gonzalez, which is herein incorporated by reference for all that it contains, discloses a multistage drag turbine assembly provided for use in a downhole motor, the drag turbine assembly comprising an outer sleeve and a central shaft positioned within the outer sleeve, the central shaft having a hollow center and a divider means extending longitudinally in the hollow center for forming first and second longitudinal channels therein. A stator is mounted on the shaft. The stator has a hub surrounding the shaft and a seal member fixed to the hub wherein the hub and the shaft each have first and second slot openings therein. A rotor comprising a rotor rim and a plurality of turbine blades mounted on the rotor rim is positioned within the outer sleeve for rotation therewith respect to the stator such that a flow channel is formed in the outer sleeve between the turbine blades and the stator. A flow path is formed in the turbine assembly such that fluid flows though the turbine assembly, flows through the first longitudinal channel in the central shaft, through the first slot openings in the shaft and the stator hub, through the flow channel wherein the fluid contacts the edges of the turbine blades for causing a drag force thereon, and then through the second slot openings in the stator hub and the shaft into the second channel.